As already mentioned pH 9 or below or a woolsafe cleaner will clean without removing protector.
My preference is Chemspec One Clean Traffic Lane Cleaner and Chemspec One Clean Liquid which has a 1:500 dilution and is recommended by all the major american carpet manufacturers for use on stain resistant carpet.
The Prochem equivalent would be Prespray Gold and Liquid Woofsafe or Fibre & Fabric Rinse
A top up coat of protector will be a profitable up-sell.